The Journal of Arthroplasty Vol. 9 No. 3 1994

Cryotherapy for Postoperative Pain Relief Following Knee Arthroplasty

Marty Ivey, MD, Robert V. Johnston, MD, and Tatsuo Uchida, MS

Abstract: Ninety consecutive patients undergoing primary knee arthroplasty received local cryotherapy 72 hours after surgery for pain relief. Thermal-pad circulating tem- peratures were randomly assigned to 50”. 60”, or 70°F (room temperature). Pain relief was monitored using patient-controlled analgesia machines. The amount of morphine received and number of attempts per hour were statistically analyzed with relation to temperature group, age, sex, weight, side, and diagnosis. The amount of morphine injected was positively correlated to the number of attempts per hour and moderately correlated to body weight. There was no correlation between thermal-pad temperature or any other parameter and the amount of morphine injected after surgery. Key words: cryotherapy, postoperative, pain, knee, arthroplasty.

The application of cold has been used extensively to decrease pain, edema, muscle spasm, hemorrhage, and the inflammatory response after injury. * Recent reports have cited the benefits of cryotherapy in the treatment of patients undergoing knee surgery for patellar problems or anterior cruciate ligament re- construction.‘,3 To determine the efficacy of cryo- therapy in reducing postoperative pain following knee arthroplasty, 90 consecutive patients were ran- domly assigned to three thermal-pad temperatures of 50”. 60”, and 70’F (room temperature). Postopera- tive pain responses were determined by the amount of morphine the patients received and the number of attempts per hour as monitored by a patient-con- trolled analgesia (PCA) machine.

Materials and Methods

This study was approved by our Institutional Re- view Board. Ninety consecutive patients undergoing primary knee arthroplasty comprised the study group. Thirty patients were assigned to each temper- ature group. A cemented, cruciate-sacrificing, poste-

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rior-stabilized prosthesis (Zimmer IB-II, Warsaw, IN) was implanted in each patient by the same surgeon. The skin incision was closed with metal staples and a single layer of gauze/cast padding dressing was ap- plied. Hot Ice thermal pads (Pro-Action Medical, Oak Ridge, TX) were applied to either side of the incision and held in place with three additional layers of cast padding and an elastic bandage. A knee immo- bilizer was applied and the thermal pads were attached distally to the Hot Ice machine (Pro-Action Medical).

Prior to the study, 30 sets of three random numbers were drawn from the uniform distribution on the interval 0, 1 using the function UNIFORM in the SAS System (Cary, NC). The three random numbers in each set were then transformed into ranks. This re- sulted in 30 sets of random sequences, each with the integers I, 2, and 3. Patients entering the study received one of three treatments according to the fol- lowing assignment: 1, 50”; 2, 60”; and 3, 70°F. For example, consider 2, 3, 1 and 3, 2, 1 as the first two sets. Using this example, the first six consecutive pa- tients would have been assigned to the temperature group in the order of 60”, 70”, 50”, 70”, 60”, and 50°F. Patients were randomly assigned, as described, to one of three temperature groups-50”, 60”, or 70°F (room temperature)-and the machine was pro-

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grammed. Patients were unaware of their assigned temperature group.

Patients were seen by a physical therapist on the morning after surgery and instructed on bed transfers and isometric exercises for all muscle groups of the operated extremity. On the second day after surgery patients ambulated weight bearing as tolerated in parallel bars. Seventy-two hours after surgery the postoperative dressing and thermal pads were re- moved and the patient started active assistive range of motion.

The operative and postoperative pain were man- aged by the anesthesia service. The choice of anes- thetic technique was at the discretion of the attending anesthesiologist. Most patients received a balanced, general endotracheal anesthetic. One patient in group 1 received a subarachnoid anesthetic. Contin- uous epidural anesthesia was performed for one pa- tient in each of the three groups. There were no anes- thetic-related complications. The quantity and type of narcotics administered during surgery were recorded. The patients were taken to the postanes- thesia recovery area, where upon awakening and presenting with pain they received intravenous mor- phine sulfate in 2 mg boluses every 10 minutes until they expressed comfort. The use of a PCA device was reviewed with the patient. The first PCA dose admin- istered was 1 mg morphine sulfate with a 1 O-minute lockout. In five instances the initial PCA settings were modified to account for patient weight or age (3 patients in group 1, 1 each in groups 2 and 3). A physician was available on a 24-hour basis to inter- vene in instances of inadequate analgesia. Such oc- currences were first treated with a bolus of 2-4 mg morphine sulfate and, if necessary, the PCA dose was increased to l$ or 2 mg. The number of PCA requests

and the number of successful administrations were stored hourly, and the data were reviewed and recorded daily. The patients remained on PCA for 72 hours after surgery.

The amount of morphine and the number of at- tempts monitored by the PCA system were averaged per hour for analysis. The linear correlation coeffi- cients (r) were computed to measure the strength of association between four response measurements: the amount of morphine injected, the number of at- tempts, age, and body weight. Twelve combinations of three explanatory factors-treatment group (50”, 60”, and 70”F), sex (male and female), and knee (left and right)-were assessed using a one-way analysis of variance procedure (ANOVA) for each of the four response measurements. Also, the two types of diag- noses (osteoarthritis and rheumatoid arthritis) were tested for those response measurements using one- way analysis of variance. All tests were performed at the P = .05 level of significance.

Results

There were no anesthetic, surgical, or medical complications. All incisions healed primarily without dehiscence, necrosis, or prolonged drainage. One Hot Ice machine malfunctioned in the recovery room and was replaced within 1 hour. Two patients in group 1 (50°F) were dropped from the study group because their postoperative records monitored by the PCA pump were lost. The patient profiles regarding age, body weight, treatment group, sex, side, and diagno- sis are listed in Tables l-3.

The amount of morphine injected was correlated to the number of attempts (r = .65) and moderately

Table 1. Patient Profile (n = 88)

Treatment 03

Sex Knee Diagnosis F M L R Osteoarthritis Rheumatoid Arthritis Total

50 16 12 13 15 27 1 28 60 19 II 17 13 28 2 30 70 22 8 15 15 28 2 30

Total 57 31 45 43 83 5 88

Table 2. Descriptive Statistics of Each Treatment Group for Age

Treatment No. of (“F) Patients

Mean Wars) (y Sk)

Minimum (years)

Maximum (years)

50 28 64.5 8.1 53 85 60 30 64.2 10.3 36 85 70 30 66.9 11.6 36 88

Cryotherapy l lvey et al. 287

Table 3. Descriptive Statistics of Each Treatment Group for Weight

Treatment (“F)

No. of Patients

Mean (lb)

Minimum (lb)

Maximum (lb)

50 2s 192 36 120 270 60 31) 182 36 107 259 70 30 188 39 118 267

Table 4. Descriptive Statistics of Each Treatment Group for Number of PCA Attempts

Treatment No. of (“F) Patients

- 50 2x 60 3(' 70 3(1

PCA, patient-controlled analgesia.

Mean (hour)

3.6 3.4 3.9

SD (hour)

2.4 2.8 3.0

Minimum (hour)

0.3 0.2 0.2

Maximum (hour)

8.4 IO.4 Il.6

Table 5. Descriptive Statistics of Each Treatment Group for Amount of Morphine Injected

Treatment No. of Mean SD Minimum Maximum C’F) Patients OWN Wg/h) Ox/h) (mg/h)

50 28 1.6 0.8 0.2 3.2 60 30 1.4 0.7 0.2 s.3 70 30 1.3 0.6 0.2 2.6

correlated to body weight (r = .47). Other pairs of the response measurements did not have notable correlations. Twelve combinations of three explana- tory factors (treatment group, sex, and knee) were not significantly different for any of the four response measurements. Thus, there were no significant differ- ences among treatment groups between sexes or be- tween knees for the amount of morphine injected and the number of attempts (Tables 4, 5; Figs. 1, 2). The same results can also be stated for age and body weight. Patients with rheumatoid arthritis tended to have a lower number of attempts and consequently a lower amount of morphine injected than patients with osteoarthritis (P -= .07 and .08, respectively). This tendency seemed to be due to a significantly lower body weight of the rheumatoid group than the osteoarthritis group (P = ,003).

Discussion

Clinically, the local application of cold progresses through four phases.4 ,4 sensation of cold is felt for 3 minutes followed by an intense burning or aching feeling up to 7 minutes. From 5 to 12 minutes numb- ness is felt followed by a deep vasodilation.

The pain-relieving effect of cold has been used for centuries.5 Hippocrates used the application of ice

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Temp (OF) Fig. 1. Average amount of morphine administered per hour versus thermal pad temperature.

288 The Journal of Arthroplasty Vol. 9 No. 3 June 1994

Fig. 2. Average number of pa- tient-controlled analgesia at- tempts per hour versus ther- mal pad temperature.

and snow to effect anesthesia prior to surgical proce- dures.6 Marco Aurelio Severino, an Italian anatomist and surgeon, applied snow in small tubes to render the skin insensible before making an incision.’ Dom- inique-Jean Larrey, Napoleon’s military surgeon, documented the numbing effects of cold in battlefield conditions of - 19°C ambient temperature, allowing him to perform amputations on soldiers.8 In 1943, Mock’ used ice bags to anesthetize donor sites for skin grafts, and in 195 1, Gibson” used a motor- driven refrigeration device for the same purpose.

The application of cold reduces pain by decreasing nerve impulse conduction and the size of the nerve action potential.’ ’ Nerve conduction is blocked when its local temperature falls below 10°C. ” Large, myelinated motor fibers appear to be affected first.“,14 Cold application helps depress the excitabil- ity of free nerve endings, thus increasing the pain threshold.15

Cold application reduces involuntary muscle spasm due to a relative deactivation of the muscle spindle. I6 The application of cold elongates latent time, contraction time, and relaxation time of muscle

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twitch.” Reports are conflicting regarding the effect of cold on local muscle blood flo~.‘~-~’ Cryotherapy can also assist with proprioceptive neuromuscular fa- cilitation techniques for stretching to improve flexi- bility.22 Hartviksen applied ice packs to decrease muscle tone in spastic muscles.23 The triceps surac muscle was examined by placing an intramuscular probe 2$ to 3f cm deep within the muscle. This probe was not affected by the application of an ice pack until 10 minutes had passed. Hartviksen noted that spasticity was decreased before the muscle tempera- ture dropped and therefore the effect was through the skin application.

The application of cold to control traumatically in- duced edema has been used empirically in the past. Matsen et al. used a rabbit model in an attempt to objectively quantify postfracture swelling by the water displacement method.‘” A circumferential water bath surrounding the extremity with tempera- tures ranging from 5” to 25°C was utilized for 96 hours. The amount of swelling observed at 96 hours increased as the water bath temperature decreased. Swelling started after the water bath was removed

Cryotherapy l key et al. 289

and was primarily localized to the subcutaneous tis- sue. This postcooling edema has been noted by other authors.15

McMaster and Liddle recognized that the clinical use of ice was not well standardized as methods of use varied widely. ” They used a rabbit forelimb crush model and measured postinjury swelling by the water displacement method to determine the op- timum application of cold. They reported that the early application of cold after injury was beneficial in decreasing edema, but that extreme cold or pro- longed use were to be avoided.

Cooling the entire body has been used to treat car- cinoma, psychiatric disorders, head injury, during cardiac surgery, and in thyroid crises.26 In addition, circumferential local refrigeration has been used for damaged extremities requiring amputation second- ary to inadequate circulation and infection.

Cold application should be avoided in patients with cold hypersensitivity syndromes.‘7,‘8 Cold should also be avoided in rheumatoid patients who have symptoms of pain and stiffness, patients who have anesthetic skin, patients who are comatose, and patients with certain athletic injuries where the anes- thetic effect of cold may block protective sensation and increase collagen stiffness. ’ 5

Cryotherapy used locally has been reported to cause peripheral nerve injury.“,” Superficial nerves, such as the ulnar nerve at the elbow, the peroneal nerve at the fibular neck, and the lateral femoral cu- taneous nerve at the iliac crest, have been affected. Recommendations for avoiding this complication in- clude the application of cold less than 20 minutes and avoidance of thcsc particular subcutaneous nerve locations. One should also avoid compression and temperatures less than 10°C and use ice massage rather than continuous compression.

In 1945, Schaubel reported on the local use of ice after orthopedic procedures in 345 patients.“’ He found that less casts wet-c cut and patients’ tempera- ture, pulse, and respiratory rates were lower than those without ice application. He noted a more nor- mal white blood cell count, fewer postoperative com- plications, and less need for narcotics.

Hot Ice thermal pads have been used to accelerate postoperative recovery and decrease the morbidity associated with surgical procedures. Water conducts heat away from an object more efficiently than air. 3 ’ Thermal pads were applied in a random, double- blind, prospective study after electrosurgical lateral release in 110 patients with patellar subluxation, pa- tellofemoral pain syndromes, chondromalacia of the patella, and patellar dislocation.” The treatment group had thermal pads at 50°F applied for 3 hours and they used a postoperative refreezable ice wrap

for an additional 20-24 hours. The treatment group had 74% good to excellent results in 1 week without complications, and the control group, which only had a compression dressing prior to tourniquet re- lease, had only 32% good to excellent results with one infection and one quadriceps muscle extrava- sation.

Hot ICC thermal pads were applied in a random fashion to patients undergoing anterior cruciate liga- ment reconstruction.3 The thermal pads were set at 50°F. The study group received pain medications that did not require many injections and were converted to oral pain medications 1.2 days sooner than the control group. There was no difference in the length of hospital stay or progression in physical therapy between the control and study groups at 6 weeks after surgery.

The effect of postoperative cryotherapy on pain re- lief was the only aspect of cold application evaluated in this study. Objective documentation of the amount of morphine administered and the number of PCA attempts per hour was readily obtained. Commer- cial marketing presentations for these products spe- cifically mention that they will reduce postoperative pain.

Previous investigators have noted that the applica- tion of ice packs to the knee joints of dogs markedly decreased the intraarticular temperature. ” Since the skin is benumbed at 50°F ( lO”C), this temperature was used as the lowest temperature in the trial groups. The ambient room temperature is close to 70°F so we arbitrarily chose this as our upper tempcr- ature. Ninety patients divided into three groups would develop statistically significant results; therc- fore, a third temperature of 60°F was arbitrarily added to the study.

One criticism of this study is that the actual circu- lating temperature of the liquid in each thermal pad was not tested and retested to document the accuracy of the machines. All machines were inspected and serviced regularly by the parent company (Pro-Ac- tion Medical).

All patients in the study group had Hot Ice thermal pads applied over one layer of postoperative dressing adjacent to the midline skin incision. The thermal pads were held in place by additional absorbent dressings and a knee immobilizer. The knee immobi- lizer and underlying dressing were kept in place for a total of 72 hours, while the patient’s pain response was monitored by a PCA machine using injectable morphine. There were no wound complications or nerve palsies from the use of the Hot Ice thermal pads. In our study only the amount of morphine in- jected and the number of attempts were correlated to the weight of the patients. The temperature of the

290 The Journal of Arthroplasty Vol. 9 No. 3 June 1994

thermal pad had no bearing on the reduction of pain after surgery. The senior author is no longer using postoperative cryotherapy for pain reduction follow- ing total knee arthroplasty.

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